1. Field of the Invention
The present invention relates to thermosetting, solvent-based resinous compositions. More specifically, the invention relates to thermosetting, solvent-based, high solids coatings comprising polyester polyols that are useful in coating both elastomeric and hard metal substrates.
2. Brief Description of the Prior Art
There are known in the art coating compositions that can be applied to elastomeric substrates. These coating compositions are characterized by excellent flexibility, particularly at low temperatures. An illustration of these coating compositions are those based on polyester-urethane polyols of relatively high molecular weight which are cured with aminoplasts. Another illustration of these coating compositions are those based on polymeric polyols such as soft polyurethane polyols cured with a stoichiometric excess of an aminoplast curing agent. Yet another illustration of these coating compositions are those based on thermosetting, hard polyester polyols, soft polyurethane polyols and aminoplast curing agents. It has been found that while these elastomeric coatings have a reasonable degree of hardness, they are not sufficiently hard to be used effectively on hard metal substrates.
Coating compositions that can be applied to hard metallic substrates are known in the art. These coating compositions are characterized by excellent hardness. An illustration of these coating compositions are those based on polyester polyols and acrylic polymers cured with aminoplasts or isocyanates. These coatings, generally, are not flexible enough to be used effectively on elastomeric parts.
In this state of the art, an article, with metallic and elastomeric parts, requires two types of coatings: one suitable for elastomeric parts and the other suitable for metallic parts. It would be recognized that a coating suitable for both metallic and elastomeric parts would be of a significant advantage in the coatings industry. Those skilled in the art would appreciate how difficult it is to prepare such coatings having, conjointly, the properties of flexibility, durability and hardness. It would be all the more difficult to prepare high solids compositions having the conjoint properties. This invention provides a high solids coating composition, the cured coating of which has, conjointly, excellent properties of flexibility, durability and hardness which make it useful on both elastomeric and hard metal parts.